Strainer of the centrifugal type



pt. 27, 1966 s. o. VALTANEN ETAL 3,275,156

STRAINER OF THE CENTRIFUGAL TYPE Filed Dec. 23, 1963 2 Sheets-Sheet 1 Sept. 27, 1956 s. o. VALTANEN ETAL 3,275,156

STRAINER OF THE CENTRIFUGAL TYPE Filed Dec. 25, 1963 2 Sheets-Sheet 2 United States Patent 3,275,156 STRAINER OF THE CENTRIFUGAL TYPE Seppo Olavi Valtanen, Olli Juhani Punttila, and Ulf Viking Sjiilund, all of Karlinla, Finland, assignors to A.

Alilstriim Osakeylititi, Karhula, Finland, :1 company of Finland Filed Dec. 23, 1963, Ser. No. 332,575 4 Claims. (Cl. 210-415) The following invention consists of a device in a strainer of the centrifugal type, particularly one used for the further alluviation of fibres such as cellulose pulps.

After it enters a centrifugal strainer, pulp is thrust by the centrifugal force towards the strainer drum surrounding the rotor, whereupon some of the fibres go direct through holes in the screen wall and the rest form a layer consisting of impurities, coarse fibres and fine fibres which cannot flow through the fibre sheet. To break up this layer, blades moving along the inner surface of the strainer drum have been used, among other devices, to create pulsations which clean the screen wall. Another method of separating utilizable fibres from the layer is to dilute those which can be diluted by adding water or fresh pulp. Alluviation water can be supplied through holes in a hollow-bored rotor shaft, for example. Such devices, in which the alluviation water flows to the periphery of the rotor through holes in the rotor shaft and from there through two plates which together form a rotor blade, are prior known. One of the drawbacks of this is that the alluviation water flows through the slit between the plates at a relatively low speed, so that the slit easily clogs up again, since the alluviation water usually consists of 0- water containing fibres. O-water is a term designating white water, that is, circulation of water (back water) of a paper factory containing small quantities of short fibres. The double blade adds weight to the rotor and makes it diflicult to clean.

The object of the invention is to eliminate the above disadvantages by means of a device in a strainer of the centrifugal type, particularly one used for the further alluviation of fibres, such as cellulose pulps. The said strainer has a rotating, hollow rotor shaft furnished with holes and with blades fastened to the shaft and running along it in a radial direction. The principal characteristic of the device is that the alluviation water and/ or pulp that enters through the rotor shaft and its holes is made to flow along the front face of each blade, as viewed in the direction of rotation, and that one the front face at the outer end of each blade near the inner surface of the strainer drum there is a detachable paddle which admits the alluviation water and/or incoming pulp on to the back face on the blade.

In the device according to the invention, the paddles attached to the rotor blades create a turbulence in the layer of fibres on the strainer drum, simultaneously causing a difference in pressure between their front and back faces, so that the alluviation water and/ or incoming pulp is effectively mixed with and alluviates the fibre layer.

Greater detail is shown in the accompanying drawings, which illustrate one embodiment of the device, adapted for a centrifugal strainer.

FIG. 1 is a longitudinal section of the strainer.

FIGS. 2 and 3 are cross sections along lines A-A and 'BB in FIG. 1.

In FIG. 1 the rotor shaft 1, which is bored hollow longitudinally in order to supply alluviation water in a manner which need not be described here, is furnished with holes 2. Pulp is fed in through an inlet 3 and, after it has been strained, it passes round the screen wall 4 and leaves through an outlet 5, while the rejected products (impurities and coarser pulp) leave through another outlet 6. Alluviation water flows through the shaft holes 2, which open on to the front faces of the rotor blades 7, and is thrust out along said front faces by the centrifugal force. Detachable paddles 8 (FIG. 2), fastened to the ends of the rotor blades 7 are shaped in such a way and placed at such a distance from the strainer drum that they create a turbulence behind them in the layer of pulp on the drum, causing a sufficient difference in pressure between their front and back faces for the alluviation water to flow through slits 9, which open on to the back faces of the paddles 8. These paddles 8 are interchangeable, so that a suitable shape of paddle can be selected for every condition of operation (quality and consistency of pulp).

Incoming pulp enters the rotor through the inlet 3. Some of the pulp in the rotor is able to flow in the direction of the arrows 10 towards the periphery of the rotor, and some or all of it passes through a cylindrical tube 11 around the shaft in the direction of arrows 12 (FIG. 1). The tube 11 is furnished with slits 12 (FIG. 3) along the front side of the rotor blades, through which the pulp is thrust by the centrifugal force and from there along the rotor blades towards the periphery, where the layer on pulp on the strainer drum undergoes further alluviation.

The paddles 8 and slits 9 can either be as long as or shorter than the rotor bladesextending from the back end of the strainer to the baflle plate 13, for example. The width of the slits 9 can be adjustable and the profile of the paddles can vary at different points along the strainer.

A device according to the invention ensures effective cleansing of the screen wall with a minimum of alluviation water and offers unlimited possibilities for adapting the strainer to different conditions of operation by changing the paddles. The invention provides greater capacity for less power consumption than conventional designs.

What we claim is:

1. A strainer of the centrifugal type adapted for the further alluviation of fibers such as cellulose pulps, comprising an elongated cylindrical perforated strainer drum, a rotatable hollow rotor shaft having a bore therein mounted coaxially of the strainer drum, means to rotate said shaft, means to admit a liquid suspension of fibers into the bore in the hollow rotor shaft, said rotor shaft having a plurality of holes through the wall thereof, a plurality of generally radially extending blades aflixed to the rotor shaft to rotate therewith within the strainer, said blades being so disposed on the shaft that the holes in the wall of the shaft lie close to and in advance of the forward faces of the respective blades which lead in the direction of rotation of the rotor shaft and blades, and a paddle mounted on the radially outer end of each of the blades, the paddles forming general prolongations of the respective blades and having their outer ends closely confronting but spaced somewhat from the inner surface of the strainer drum, the paddles and blades at the zone of connection therebetween presenting openings therethrough whereby said liquid suspension is caused by centrifugal force to flow along the forward faces of the blades, out through said openings at the connections between the outer ends of the blades and the paddles, and into contact with fibers collected on the inner surface of the strainer, in order further to alluviate such collected fibers.

2. A strainer as claimed in claim 1, wherein said openings at the zone of connection between the radially outer ends of the blades and said paddles are in the form of slits disposed at an acute angle relative to the main extent of the blades and inclined in a direction radially outwardly and rearwardly thereto with respect to the direction of rotation of the shaft and blades.

3 4 3. A strainer as claimed in claim 1, wherein said References Cited by the Examiner paddles have an axial length which is substantially the UNITED STATES PATENTS same as that of the blades and strainer, and both the blades ancll padglles lie radially within the strainer through- 5 if z i fi' ellgt 3,149,067 9/1964 Cannon et al. 210 415 X 4. A strainer as claimed in claim 1, comprising a housing surrounding and radially spaced from the strainer, REUBEN FRIEDMAN, Primary Examiner.

and liquid discharge means connected to the housing. L DECESARE Assistant Examiner 

1. A STRAINER OF THE CENTRIFUGAL TYPE ADAPTED FOR THE FURTHER ALLUVIATION OF FIBERS SUCH AS CELLULOSE PULPS, COMPRISING AN ELONGATED CYLINDRICAL PERFORATED STRAINER DRUM, A ROTATABLE HOLLOW ROTOR SHAFT HAVING A BORE THEREIN MOUNTED COAXIALLY OF THE STRAINER DRUM, MEANS TO ROTATE SAID SHAFT, MEANS TO ADMIT A LIQUID SUSPENSION OF FIBERS INTO THE BORE IN THE HOLLOW ROTOR SHAFT, SAID ROTOR SHAFT HAVING A PLURALITY OF HOLES THROUGH THE WALL THEREOF, A PLURALITY OF GENERALLY RADIALLY EXTENDING BLADES AFFIXED TO THE ROTOR SHAFT TO ROTATE THEREWITH WITHIN THE STRAINER, SAID BLADES BEING SO DISPOSED ON THE SHAFT THAT THE HOLES IN THE WALL OF THE SHAFT LIE CLOSE TO AND IN ADVANCE OF THE FORWARD FACES OF THE RESPECTIVE BLADES WHICH LEAD IN THE DIRECTION OF ROTATION OF THE ROTOR SHAFT AND BLADES, AND IN PADDLE MOUNTED ON THE RADIALLY OUTER END OF EACH OF THE BLADES, THE PADDLES FORMING GENERAL PROLONGATIONS OF THE RESPECTIVE BLADES AND HAVING THEIR OUTER ENDS CLOSELY CONFRONTING BUT SPACED SOMEWHAT FROM THE INNER SURFACE OF THE STRAINER DRUM, THE PADDLES AND BLADES AT THE ZONE OF CONNECTION THEREBETWEEN PRESENTING OPENINGS THERETHROUGH WHEREBY SAID LIQUID SUSPENSION IS CAUSED BY CENTRIFUGAL FORCE TO FLOW ALONG THE FORWARD FACES OF THE BLADES, OUT THROUGH SAID OPENINGS AT THE CONNECTIONS BETWEEN THE OUTER ENDS OF THE BLADES AND THE PADDLES, AND INTO CONTACT WITH FIBERS COLLECTED ON THE INNER SURFACE OF THE STRAINER, IN ORDER FURTHER TO ALLUVIATE SUCH COLLECTED FIBERS. 